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Photometry & Radiometry Metrology

The photometry and radiometry group of the NML maintains the national measuring standards of light for South Africa in the fields of:

A contract with the Department of Trade and Industry allows us to maintain these measuring standards on an international level. The country's standard of optical radiation (light), an absolute radiometer system, was designed by the engineers and scientists of the project and has been sold to national laboratories in Taiwan, New Zealand, Italy, Argentina, Spain and the BIPM in France. A cryogenic radiometer is being phased in as a new national standard for optical radiation.

We constantly strive to improve our measuring expertise, instrumentation and standards in order to ensure that the South African industry and research and educational institutions have access to international competitive measuring facilities at an affordable price. An extensive list of capabilities exists in each of the fields listed above. Apart from numerous standard services we offer, every effort is made by staff to meet client's needs by designing fit-for-purpose optical set-ups.

We are actively involved in the relevant national and international committees and working groups in the field op photometry and radiometry to maintain current expert knowledge. These include, amongst others, the International Commission on Illumination (CIE), the International Electrotechnical Commission (IEC), the International Colour Association (AIC), the South African National Committee on Illumination (SANCI) and the Colour Group of the South African Optical Society.

RADIOMETRY

The national irradiance scale is realised by means of electrically calibrated radiometers, which measure radiant power by comparing its heating effect to that of substituted electrical power.

Measurements can be made of the responsivity (also spectral responsivity in the range 400 nm to 1,600 nm) and linearity of optical radiation detectors (thermal and photo-electric). Some of the more common types of measurements performed are the calibration of irradiance meters, radiant power meters and pulse energy meters.

Various tests, as specified by the Department of Health and National Population Development can be done on CW and pulsed lasers in order to determine the classification of laser devices.

Contact Person: MD (Meena) Lysko, Dr. Scient.
Tel: +27 12 841-2424

PHOTOMETRY / GONIOPHOTOMETRY

The national photometric scale is derived from the national radiometric scale using the definition of the candela and the spectral response of the standard human eye. It is realised by measuring an unknown light source with an electrically calibrated radiometer through a filter, giving it nominally the same spectral response as the CIE standard photometric observer for photopic vision.

The scale for total luminous flux is derived from the scale for luminous intensity by means of a spatial integration performed with our in-house designed goniophotometer.

Illuminance meters (lux meters) can be calibrated against working standards of luminous intensity. In the case of the calibration of luminance meters, known luminances are produced by illuminating a barium sulphate tablet with a source of known luminous intensity. Lamps can be calibrated for distribution temperature (colour temperature) luminous intensity, illuminance at a specified distance or total luminous flux. A small stock of aged lamps is kept and is available for sale to customers.

Contact Person: Margaret Budzinski
Tel: +27 12 841-4817

SPECTRORADIOMETRY

Sources of optical radiation can be calibrated in terms of their spectral irradiance (250 nm to 1,600 nm) at a specified distance in a given direction and the relative spectral power distribution of sources can be determined. From the spectral data specific parameters can be derived, like colour coordinates, colour temperature, effective erythemal irradiance (UV sources) and RCEE values for SPF sources.

Contact Person: LAG (Berto) Monard, Pr Eng
Tel: +27 12 841-3003

SPECTROPHOTOMETRY

Facilities exist for the measurement of the spectral transmittance and reflectance of materials in the wavelength range 200 nm to 2 600 nm (direct transmittance) and 350 nm to 1 500 nm (diffuse transmittance, specular reflectance and diffuse reflectance). Thermal and optical properties of materials for luminous or solar irradiance can also be determined.

Absorbance and peak transmission wavelengths of materials can be measured. These materials can then be used to verify the wavelength scale of various devices, for example spectrophotometers and spectral analysers.

Contact Person: EM (Elsie) Coetzee, B Sc
Tel: +27 12 841-3047

COLORIMETRY

Colours of light sources or illuminated objects are specified in terms of CIE chromaticity co-ordinates x, y and z. (It can also be transformed to various other colour spaces). The luminance factor L can also be determined. For non self-luminous objects, the chromaticity co-ordinates also depend on the specified illuminant, and can be calculated for all CIE Illuminants.

Chromaticity co-ordinates are calculated either from the relative spectral power distribution of the source alone or from the source combined with the spectral reflectance or transmittance of the test sample. Colorimeters are colour measuring devices that measure the chromaticity co-ordinates of colour surfaces or sources. Cathode Ray Tube (CRT) colorimeters can be calibrated at colour temperatures ranging from 5,500 K to 9,500 K.

Colour differences between specified surface colours can be determined and surface colours can also be specified in Colour Order Systems, such as the Natural Colour System (NCS) or the Munsell system.

Contact Person: EM (Elsie) Coetzee, B Sc
Tel: +27 12 841-3047

ULTRAVIOLET RADIOMETRY

Ultraviolet radiometry forms an integral part of radiometric and spectroradiometric measurements but is mentioned separately as this field requires additional expertise and facilities. This special category covers the calibration of ultra violet measuring instruments and ultra violet sources. Irradiance and dose calibration are offered and traceability is obtained via the radiometric standards and working standards. Measurements are offered for each of the three ultra violet regions:

In addition to UV, traceability is also provided for blue light meters and lamps, specifically those used for blue light therapy.

Contact Person: L A G (Berto) Monard, Pr Eng, M Sc (Mech) Eng
Tel: +27 12 841-3003